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| Lower Jurassic | |
|---|---|
| Name | Lower Jurassic |
| Start | 201.3 Ma |
| End | 174.1 Ma |
| Era | Mesozoic |
| Period | Jurassic |
Lower Jurassic The Lower Jurassic marks the earliest epoch of the Jurassic Period, beginning after the end-Triassic crisis and preceding the Middle Jurassic. It encompasses major recoveries and radiations following the Triassic–Jurassic extinction event, and records key developments in marine and terrestrial ecosystems, plate reconfiguration, and early Jurassic paleontology research. The interval is central to studies by institutions such as the Geological Society of London, the Natural History Museum, London, and the Smithsonian Institution.
The Lower Jurassic spans the Hettangian, Sinemurian, and Pliensbachian stages and is framed by biostratigraphic markers used by the International Commission on Stratigraphy and regional surveys by the British Geological Survey. Prominent historical investigations include fieldwork by figures associated with the Geological Survey of Great Britain and paleontological synthesis in monographs from the Palaeontological Association. Geological mapping in areas like the Dorset Coast and the Southerham Reclamation has shaped modern interpretations. The epoch is commonly referenced in global correlations such as the Tethys Ocean reconstructions and regional chronologies developed by the United States Geological Survey.
Formal subdivision follows stage-level units recognized by the International Commission on Stratigraphy: Hettangian (base), Sinemurian, and Pliensbachian (top of the Lower Jurassic). Regional schemes incorporate lithostratigraphic units such as the Lias Group in the United Kingdom, the Posidonia Shale equivalent successions in Germany, and the Sinemurian facies of the Paris Basin. Biostratigraphic zonation uses index fossils documented by researchers at the Muséum national d'Histoire naturelle and the Natural History Museum, Berlin. Correlation methodologies involve ammonite zonation refined since studies by the Geological Society of America and chronostratigraphic charts by the International Union of Geological Sciences.
Paleogeographic reconstructions place continental configurations influenced by the breakup of Pangaea and the evolution of the Tethys Ocean, with paleomaps developed by teams at the Paleomap Project and researchers affiliated with the University of Chicago. Global sea-level changes and regional transgressions affected coasts in the North Sea Basin, the South Atlantic embryonic rift, and the Western Interior Seaway precursors studied by the United States Geological Survey. Climate interpretations derive from isotopic work published by scholars at the Max Planck Society and the University of Oxford, indicating greenhouse conditions with regional variability and monsoon-like patterns referenced in syntheses by the Intergovernmental Panel on Climate Change authorship teams.
Fossil assemblages include marine invertebrates—ammonites, belemnites, bivalves—documented in collections at the Natural History Museum, London and the Senckenberg Museum. Vertebrate records feature early neosauropod and theropod dinosaurs reported from sites investigated by the University of Cambridge and the University of Oxford teams, as well as marine reptiles such as ichthyosaurs and plesiosaurs cataloged by the British Museum (Natural History). Plant macrofossils and palynological records housed at the Royal Botanic Gardens, Kew and the Smithsonian Institution indicate gymnosperm-dominated floras with ferns and early conifers analyzed by researchers affiliated with the Royal Society. Lagerstätten like those studied by the Senckenberg Research Institute preserve exceptional fossils that have informed taxonomic revisions in monographs issued by the Palaeontographical Society.
Sedimentary facies range from siliciclastic shelf deposits to organic-rich black shales and carbonate platforms explored in the Cleveland Basin and the Paris Basin. Detailed sedimentary logging and sequence stratigraphy approaches were advanced by scientists at the University of Texas at Austin and the Shell Oil Company petroleum geology groups. Fluvial, deltaic, and shallow marine systems recorded in the Mercian Basin show cyclicity tied to eustatic fluctuations chronicled in regional reports by the British Geological Survey and the Norwegian Petroleum Directorate.
Lower Jurassic strata host hydrocarbon source rocks and reservoirs such as the Posidonia Shale analogues evaluated by the Norwegian Petroleum Directorate and the Oil and Gas Authority (UK). Building stones and clays from the Dorset Coast and the Cotswolds have been quarried historically and cataloged by the Historic England agency. Key paleontological localities include the Lyme Regis and Whitby areas where collectors influenced early fossil science associated with the Geological Society of London and collectors documented in archives at the Natural History Museum, London.
Age models integrate ammonite biostratigraphy, radiometric dates from volcanic ash layers analyzed at facilities such as the Geological Survey of Canada and the United States Geological Survey, and magnetostratigraphy applied in collaborative projects with the International Ocean Discovery Program. Chronostratigraphic charts published by the International Commission on Stratigraphy and synthesis volumes from the Cambridge University Press provide the standard temporal framework used in global correlations and basin studies.